1. Field of the Invention
The present invention relates to measurement of errors of a quadrature modulator.
2. Description of the Prior Art
Conventionally, it has been known that errors of the quadrature modulator include a gain imbalance and a quadrature error.
Referring to abstracts of Patent Document 1 and Patent Document 2, there are descriptions that a phase difference of a signal modulated by a sub carrier is to be obtained. However, though these descriptions mention that the phase difference of the modulated signal is obtained, obtaining phase difference is different from obtaining a quadrature error of quadrature modulation (namely, difference between a phase difference between an I signal component and a Q signal component of a modulated signal and 90 degrees).    (Patent Document 1) WO 2007/072653 pamphlet    (Patent Document 2) WO 2007/077686 pamphlet